Sunday, April 10, 2016

When people use the word "consciousness", they can be referring to many things. At a simple level, they could be referring to being simply awake, or having some awareness of the world. At a more complex level, they could be discussing awareness of one's own self. But there is another thing people talk about when they speak of consciousness-the ineffable sense of what it is like to be oneself. It seems reasonable to most people that the human brain should be capable of dealing with waking, as well as the harder task of thinking about one's own cognition.

However, it is less popular to think that the brain can produce this intangible feeling that we can only really observe in ourselves. Many people believe that this feeling will continue after death has taken our fleshy brain from us. Some people believe that the scientific study of consciousness will progress better if we treat consciousness as a fundamental property, something which cannot be broken down into something simpler, such as the biological and chemical processes underlying brain function (much like electric charge became seen to be a fundamental property in the 19th century,).

However, if our conscious experience really is just the product of our feverish brains, than perhaps theholy grail of neuroscience is to find what it is in the brain that brings this about...

The neural correlate of consciousness!

A cool paperby Naotsugu Tsuchiya and colleagues discusses the search for correlates of consciousness with and without self-report. Self-report can be combined with clever methods used to make the same sensory input, depending on context, available or unavailable to awareness. Continuous flash suppressioninvolves presenting one eye with a flashing stimulus and the other eye with a more constant stimulus. The flashing stimulus can lead to the other stimulus (which, remember, doesn't change) slipping out of consciousness, even though the sensation should still be there.

So let's say you're a research participant being subjected to continuous flash suppression. The experimenters need you to tell them what you're consciously perceiving, in order for them to observe what is happening in your brain as the subjective experience changes. However, in order to self-report on what one perceives, one needs to draw on cognitive processes other than "raw" consciousness. If you have to say what you see, you're using language processing. If you have to press a button when you see the white elephant, you need to use motor processing. Control conditions have to be carefully designed!

So there are a number of caveats about self-report. Methods that do not use self-report are not perfect either though-it's harder to tell whether the thinker is really (self-)aware of the information they're processing. However, what's really neat about a lack of self-report is that it can be applied in contexts where self-report may be difficult or impossible, for example in babies or in animals.

Of course, you might object that much of this is just about the not-so-hard problems of how we are aware or self-aware, not about what consciousness is like. I think this takes us from the methodology we use to study consciousness, to our account of what "ineffable" consciousness is about. Our subjective sense of what experience is like involves combining a wide variety of sensory inputs (not to mention memories, body schemas etc. etc.) into a unitary experience. The binding problem poses the question of how we perceive our experience as a unified stream of consciousness.When we talk of a "neural correlate of consciousness" it's probably too simple to think that one part of the brain can "bring it all together". In order to integrate various sensory inputs together we have to combine sensory processing occurring in distinct regions of the brain. Gerald Edelmanhas suggested that the thalamus plays a key role, as it carries information from the senses to various parts of the cortex. It is the re-entrant nature of these connections that may help to explain the process (as opposed to the place) where experience comes together to make up a unitary sense of consciousness.

You may hold fast to the idea that your experience cannot be just the product of your brain (and its interaction with the rest of your body). But if so, let me pose this question: just how complex is your conscious experience really? Are you sure it is more complex than the interactions of the trillions of neurons in your brain? If you or someone else really understood how it all worked, are you so confident that they might not be able to explain your lived experience, with no need to discuss anything outside the biological and chemical processes within you?

Saturday, April 2, 2016

I tried to read my school books despite the fact
that my mind wandered a thousand miles away. I would come back to whatever I
had been reading wondering to myself where I had been for the last five or ten
minutes. It was not that I could not remember what I had read. Rather, I had
never read the page I was staring at for that period of time. (Allan Schwartz, 2007)

This account of ADHD is something most people can identify with to some extent. Going over a lecture on attention for a neuroscience module at UCC, I'm thinking again about sustained attention. What can neuroscience tell us about how we focus our minds on a particular stream of information?In studying sustained attention, a typical experimental task will ask participants to attend to a fairly boring set of stimuli for a prolonged time and produce a periodic response to an occasional target stimulus (e.g. a repetition of a number in a series of generally non-repeating numbers). Cognitive psychology giant Michael Posner and colleagues have suggested that the right cortex is key
for this form of attention. However, other research has suggested that when a target is less
salient (which made the task more difficult), activation was bilateral (i.e.
activation occurred on both sides of the brain). It's a reminder that the nature of a task is key in the brain activity involved. Indeed, given that sustaining attention to such a task becomes more difficult as time goes by, the same task becomes a more difficult job over time within the same person.

Isn't it almost redundant to say you need motivation to sustain attention on something? If something is interesting then it's inherently motivating to attend to it, but if it's boring you need something to threaten/entice you into attending to it. Given its influence on the reward system, it has been suggested that dopamine may influence sustained attention through its
impact on motivation. Methylphenidate (often sold under brand name “Ritalin”) is used in the treatment of ADHD, and it is used to increase the extracellular level of dopamine. Speaking of dopamine-our familiar friend caffeine, which enhances dopamine, has been shown to enhance subjective
alertness and improved sustained attention performance on a simulated driving task. However, as most people consume caffeine,
experimental control is required to ensure that any effects are not due to withdrawal reversal. If you want to run a study on caffeine effects, you can ask people taking part to avoid caffeine for long enough before a study for any caffeine to have left the body. So now you can say that if you give 200mg of caffeine it's not being added to another 200mg the person drank an hour ago. However, long enough to get caffeine out of the system is not necessarily long enough for withdrawal symptoms to have passed. So there is a risk that the enhancing effects are only shown because you give a
person caffeine when they are withdrawn. I should note that there has been some debate about the extent to which withdrawal reversal has confounded research on caffeine, including evidence to the contrary. Evidence for a role for noradrenalin comes from the spontaneously hypertensive rat (SHR). As the name suggests, it is prone to high blood pressure. However, it can also act as a model of ADHD-although it has its critics, this type of rat has been shown to demonstrate a number of traits associated ADHD (including impulsiveness as well as inattention).Noradrenalin has been implicated in the ADHD-like behavior of this rat by the alteration of such behavior by the noradrenergic drug Guanfacine.I can close with a quick tip on sustaining attention, as someone who has had his mind drift far away at many a lecture. When I decide I really need to focus on a talk, I try to think of a question as early on as possible in the talk. I then try to see if anything in the talk answers this question. Whether or not I will actually ask the speaker this question aloud, I imagine that I will have to ask it, and thus motivate myself not to look foolish by asking a question that has been answered by the content of the talk. I don't have any great solution for when one is sleep-deprived and heavily sleepy though-suggestions welcome!Related posts: